Question

Mixing of entering and exit fluid does not occur in which one of the following reactors?

• A. Batch flow
• B. Plug flow
• C. Mixed Flow
• D. Semi batch

Hint:

In a plug flow reactor (PFR), fluid moves like a series of individual "plugs" with no back-mixing — ideal for maintaining concentration gradients.

Answer 1

The Correct Option is B

A Plug Flow Reactor (PFR) is characterized by the assumption that fluid flows through the reactor in a series of "plugs" or thin layers without axial mixing.
Each infinitesimal element of fluid entering the reactor progresses through it without mixing with elements ahead or behind.
In other words:
- There is no mixing in the direction of flow (axial direction).
- Each plug behaves as an isolated entity with uniform composition.
- This ensures that the entering fluid does not mix with the exiting fluid.
Let’s examine the incorrect options:
- Batch flow: No flow enters or leaves during operation, but complete mixing occurs within the vessel.
- Mixed flow (CSTR): Perfect mixing is assumed, so entering fluid instantly mixes with the reactor contents.
- Semi-batch: Involves addition of one or more reactants during reaction — partial or full mixing is common.
Hence, the only reactor where no mixing occurs between entering and exiting fluid is the Plug Flow Reactor.